Baumeister calls it a “rediscovery” because willpower is a concept that has been understood with varying degrees of accuracy through the years. Since ancient times, it was cursorily understood as a “power” unto itself; something to be harnessed and exercised. This is called the “energy model” of willpower. The energy model was incorporated by Freud into the “superego”.

The energy model fell out of fashion when Freud did, until very recently when psychologists started comparing notes with biologists. They noticed patterns in body rhythms and nutrition that corresponded with the psychological ability to self-regulate. It turns out that our ancient understanding of willpower as an energy unto itself was closer to the truth than we thought.

Willpower 101: How It Works

Here’s a synopsis of what scientists know so far:

Roy Baumeister, Florida State University

Whenever we exert mental effort–thinking about a hard problem, resisting a temptation, making a tough decision, stressing about a looming deadline, controlling an emotional response, or anything that Kahneman would call “System 2 Thinking”–we deplete a finite resource of energy. There are other processes that drain this resource as well, like our immune system when we’re sick. All these different forms of exertion draw from the exact same pool of energy, so if you deplete yourself by making a lot of tough decisions, you have less mental energy left over to, say, stick to a diet. Psychologists call this “ego-depletion”.

Ego-depletion is related to blood sugar levels, but the exact metabolics are hard to pin down. We know that willpower generally raises and lowers with blood glucose levels. Your brain, like your muscles, uses various forms of glucose in the body as fuel. It takes glucose directly from the bloodstream and also stores it locally in the form of glycogen.

We don’t really know the metabolism structure of the brain yet, because until recently you couldn’t analyze brain glycogen levels without killing the subject. But we know how it works with our muscles, and the process may be analogous. When oxygen is readily available in the blood, our muscles will feed off of blood sugar. When oxygen is not readily available, they instead draw from local glycogen stores (which don’t require external oxygen to burn). When local glycogen stores in the muscles are used up, muscles refuse to work. Athletes call it “bonking” or “hitting a wall”. The brain might do the same thing for the same reason.

WILLPOWER!

You don’t need to understand the physiology to understand ego-depletion, but this knowledge helps when trying to counteract the effects. The key to greater mental energy might lay, for example, in training up the amount of glycogen stored in the brain. Alternately, it might lay in building up efficient oxygenation in the body so that the brain can burn more blood glucose and less glycogen.

Whatever the neurological specifics, we know that our reserves of mental energy and willpower are drained through various kinds of mental exertion and restored by nutrients and sleep.

We Can Only Give So Much…

When we are in an ego-depleted state, we suffer in our ability to self-regulate. We have less energy for impulse or emotional control. The world seems more melodramatic. Emotions seem more powerful. We make different decisions because we’re more reluctant to give up options. There was a famous experiment dealing with parole judges in Israel, in which it was discovered that a potential parolee had a significantly better chance of being granted parole if he appeared in court soon after the judges and eaten a meal. In a depleted state, judges would be less apt to grant parole because that’s a decision that reduces options; if you deny parole, you still have the option to grant it to the same prisoner at a later date.

Sample Causes of Ego Depletion

This information can help dispel some common myths. One myth, for example, is that there are certain people who are just blessed with iron wills, and we mere mortals are doomed to failure. This is like saying that some people are just born with iron muscles. Genetics are a contributing factor in muscle building, but no one is born in peak athletic condition.

This information also debunks the usefulness of diets that restrict certain foods, because as soon as we name a certain food as our enemy we start burning up all our energy just thinking about avoiding it. The food, which used to be meaningless, is now a stressor.

We should understand that willpower reserves are depleted by many kinds of mental effort and stress, so you might experience depleted willpower after not having being tempted by anything all day. We should also understand that external influences, like alcohol consumption, can further blunt our ability to self-regulate. We cannot rely on our willpower to be there for us 100% of the time.

The biggest problem, therefore, comes when we rely only on our flaky, finite powers of self-control to keep us away from the things we know we should avoid. If you leave candy sitting around, you cannot always count on your self-control to keep you away from it, and you burn self-control energy just thinking about it.

Those who are most successful in sticking to disciplines and regimens are those who use their limited self-control to structure their lives proactively and establish healthy habits. Habits and planning are much, much more powerful and reliable than willpower alone.

Ariely points out that there are things that we can do in the short term to boost willpower. Good regulation of blood sugar in the body (like avoiding spikes and crashes) will improve our willpower, as will pre-planning certain indulgences so as to counteract the stress of avoiding them. It may even be that consistent exercise boosts mental energy and willpower by enlarging brain glycogen stores and/or improving bodily oxygenation.

But if we really want to master willpower, we must channel whatever limited amount we have into structuring consistent habits and routines for ourselves, including pre-planned deviations or indulgences. We must use our limited resources where they will do the most good.